For bolted connection, the main reason for looseness is: when the bolt bears transverse (perpendicular to the bolt axis) vibration load, with the increase of the vibration force, a friction coefficient between bolt pairs is even decreased to zero, thereby damaging self-locking condition of the thread, generating slight relative slide and causing automatic rotation and looseness of the nut. In some extreme cases, the looseness of the transverse load may decrease the bolt preload by 30%-40%. The testing machine for the looseness of the transverse load can be used to research a looseness law under the condition that the bolt bears horizontal alternating load, and is very useful for researching the looseness problem of bolted connection.
The present invention is based on the testing machine for accurately controlling the looseness of the transverse load bolt. A load control part is added on the testing machine for accurately controlling the looseness of the transverse load on the basis of an original testing machine for looseness of Junker transverse load bolt, so as to better control the transverse load.
1. Ensuring Transverse Displacement Load
For the previous testing machine for looseness of the transverse load bolt, the testing machine can only provide a transverse displacement load. If the displacement load is required to be changed, the mechanical structure of the testing machine must be changed, which is high in cost and is difficult. It can be known from FIG. 1 that a fixed x value corresponds to a unique y value. Through rotation of the load control motor 17, the screw rod 16 is driven so as to drive the slide table 18 to move up and down. Namely, displacement is produced at the end of the rocking bar 20. If the x value is changed, the maximum amplitude of the generated transverse displacement is also changed. Each position at the end of the rocking bar 20 represents the maximum amplitude of one transverse displacement. A desired transverse displacement can be obtained through the control motor 17.
2. Ensuring Transverse Force Load
When the testing machine provides a transverse displacement amplitude, a transverse force load will be generated simultaneously. Along with the occurrence of looseness, the transverse force load generated by the fixed transverse displacement is gradually decreased. At this moment, if a fixed transverse force load needs to be unchanged, the generated transverse displacement amplitude shall be gradually increased. At this moment, the control motor increases the generated transverse displacement load until the force measured by an S-shaped column type tension sensor reaches a predetermined value.
How to control the above test bench to enable the test bench to achieve expected functions becomes a technical problem which must be solved in the art. Accurate control over the transverse load can be realized only based on an appropriate control method and control program.